Hansen Dam Sediment Modeling Study Impact of Water Supply vs. Flood Control Operational Modes on Sediment Deposition in the Reservoir Area

The analysis of scour and deposition in Hansen Reservoir by modeling the interaction between the water-sediment mixture, sediment material forming the stream's boundary and the hydraulic characteristics of flow is presented in this paper using Hydrologic Engineering Center's HEC-6 Computer program entitled 'Scour and Deposition in Rivers and Reservoirs. ' The results of the analysis can be used for estimating the impact of differing modes of reservoir operation - flood control vs. water supply - on reservoir sedimentation. Model results indicate that the amount of deposition corresponding to water supply option would be approximately ten percent higher than that for the flood control operating policy. Furthermore, this additional sediment material would be composed predominantly of cohesive silts and clays that would deposit in the lower reaches of the reservoir area in the vicinity of the outlet.